Stabilization of formaldehyde solutions



United States Patent 0.

3,137,736 STABILIZATION F FORMALDEHYDE SOLUTIONS Roy H. Prinz, Robstown, and Bob C. Kerr, Kingsville,

Tex., assignors to Celanese Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed May 18, 1959, Ser. No. 811,250

. 12 Claims. (Cl. 260606) This invention relates to formaldehyde and particularly to the stabilization of concentrated aqueous solutions of formaldehyde.

Aqueous solutions of formaldehyde of over 30% concentration tend to become cloudy, with the formation of formaldehyde polymers. It has long been known that it is desirable to have more highly concentrated solutions of formaldehyde in order to save the expenses of shipping and handling large quantities of Water with the formaldehyde. To this end methanol has been added as a stabilizer. Thus ordinary commercial formaldehyde, containing 37% formaldehyde by weight, generally contains about 8 to methanol to prevent precipitation of polymers. The presence of such large amounts of methanol is not always desirable, since it interferes with some reactions in which formaldehyde is employed. In addition, even when the methanol has no deleterious effect, the presence of an appreciable proportion of this material, serving only a stabilizing function, necessarily adds to the cost of the solution. Also, even with such large amounts of methanol the concentration of formaldehyde obtainable in a stable solution is not as high as desired.

It is therefore one object of this invention to produce stable concentrated formaldehyde solutions of relatively low methanol content.

Another object of this invention is the provision of novel stabilizers for formaldehyde, which stabilizers are effective even when present in very small proportions.

Other objects of this invention will be apparent from the following detailed description and claims. In this description and claims all proportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention aqueous formaldehyde has incorporated therein a colloid which acts to stabilize the solution. Advantageously the colloid used is one which is soluble in the aqueous formaldehyde without coloring or clouding the formaldehyde solution. A particularly suitable colloid is a cold water soluble methyl cellulose such as hydroxypropyl methyl cellulose or methyl cellulose, per se. Examples of other colloids which may be employed include such high polymers as gelatin (e.g. calf gelatin or pig gelatin), pectin and Irish moss extractive (carrageenin). Of the hydroxypropyl methyl celluloses which have been tested, excellent results have been obtained with those having a viscosity (when dissolved at 2% concentration in water at 25 C.) of at least 3000 e.g. 3000-5000 centipoises, a methoxy content of about 27 to 30% and a hydroxypropyl content of about 412%. Excellent results have also been obtained withmethyl cellulose having a methoxy content of 26-33% and a viscosity (when dissolved at 2% concentration in water at 25 C.) of about l200l0,000 cps. Good results have also been obtained by the use of ethyl cellulose (for instance ethyl cellulose of 4849.5% ethoxy content) and by the use of such colloidal materials as lipophilic polyoxyethylene ethers of higher fatty alcohols such as lipophilic polyoxyethylene lauryl ether (e.g. Brij 30, a colorless oily liquid having an HLB, Atlas, of 9.5; a viscosity at 25 C., of 30 cps., a specific gravity of 0.95, soluble in toluol, acetone, methanol and mineral oil, insoluble in 5% H 80 and lipophilic sorbitan esters of higher fatty acids, such as sorbitan monolaurate (e.g. Arlacel 20, a lipophilic yellow oily liquid having an HLB,

Patented June 16, 1964 Atlas, of 8.6, a viscosity at 25 C. of 5000 cps., soluble in mineral oil), but these materials do not stabilize as effectively, or at such low concentrations as those mentioned previously. Other materials having an inhibiting effect, but usually producing a somewhat cloudy solution, are cellulose mixed esters such as mixed esters of cellulose and higher fatty acids, e.g. cellulose acetate stearate.

The proportions of colloid may be very small. For example one hydroxypropyl methyl cellulose which is very effective does not dissolve completely uniformly in aqueous formaldehyde When the colloid is present in amount of 500 ppm. (based on the weight of the solution); that is, the colloid-containing solutions at this concentration and at higher concentrations (e.g. 1000 ppm.) although clear, have a granular appearance. This colloid is found to be an excellent stabilizer even at much lower concentrations, for example less than ppm, e.g. 10 p.p.m., and these lower concentrations are more desirable since the resulting solutions have less tendency to foam. Even with more soluble colloids it is usually preferable to use very small amounts, generally less than about 0.5% of dry colloid (based on the Weight of the solution). Preferably the amount of colloid is such that the addition thereof has no substantial effect on the viscosity of the formaldehyde solution.

The concentration of formaldehyde is desirably above 30%, since with lower concentrations the problem of stability is not significant. The present invention makes possible stable formaldehyde solutions of well over 40% concentration, even when little or no methanol is present.

The stability of aqueous formaldehyde depends, as is well known, on the temperature. A solution which is not stable when stored at room temperature may remain substantially unchanged when stored at higher temperatures, e.g. 50 C. Similarly, cooling of concentrated aqueous formaldehyde decreases its stability and causes the formation of solid polymer. Like ordinary concentrated aqueous formaldehyde solutions, the solutions of the present invention may be solidified to form a paste, or in some cases, a slurry, by holding them at a low temperature for a sufficient time and may then be reliquified by heating. However, with the solutions of the present invention the reliquefaction takes place Without the formation of any substantial quantity of insoluble polymers of formaldehyde, even after many cycles of solidification and liquefaction. In contrast when conventional concentrated formaldehyde solutions are solidified in this manner a considerable residue of insoluble polymer is formed, the amount of insoluble polymer increasing with each cycle of solidification and liquefaction.

The solutions of the present invention may be used for the same purposes as conventional solutions of formaldehyde. When reacted with urea, they have the further advantage of yielding resins of improved clarity.

If desired, the aqueous formaldehyde may be treated, before or after the addition of the hydrophilic colloid, to remove ions therefrom. Such ions may be metallic ions (e.g. iron) picked up by the solution as a result of contact with metallic equipment, or formate ions resulting from the Cannizarro reaction in which two molecules of formaldehyde react to form a molecule of formic acid and a molecule of methanol. Removal of ions may be effected by passing the solution through one or more ion-exchange resins. Anion exchange remains, alone or in combination with a cation exchange resin treatment may be employed, as is conventional in the art. Solutions from which the ions have been removed have improved stability.

The formaldehyde solutions of high concentration may be produced in well known manner, as by dissolving gaseous formaldehyde or solid paraformaldehyde in water, or by vacuum concentration of dilute aqueous formaldehyde,

concentrated).

' cycles.

or 'by pressure distillation of dilute aqueous formaldeenemas overhead, or by any suitable combination of these. The

colloids used in this invention may be conveniently dissolved in the freshly prepared concentrated solutions (or, when appropriate, maybe dissolved in the solution being cipitation of the dissolved colloid; similarly, any anions or cations which tend to precipitate the colloid should be avoided, for best results. The following examples are given to illustrate this invention further.

Example I (a) vTo a freshly prepared aqueous40% solution of Q formaldehyde (produced as a product .of the partial oxidation, with air or oxygen, of an aliphatic hydrocarwas stored at a temperature of 30C. for a period of over 8 weeks without any observable polymerization. An identical sample without-the hydroxypropyl methyl cellulose showed evidence of polymerization within. 24 I hours whenstored under the same conditions.

(b) The hydroxypropyl methyl cellulose-containing solution was shipped at low winter temperature for a' period of several days, and formed a slurry or paste. On gentle heating this paste dissolved to give a brilliantly clear solution which remained stable at room temperature, even after several months.

Example II The fresh colloid-containing solution of Example I was heated under a subatmospheric pressure of 70 mm. Hg absolute until its formaldehyde concentration was increased to 50%. The resulting solution remained stable when stored for over 4 weeks at a temperature of 38 C. An identical sample without the hydroxypropyl methyl cellulose showed evidence of polymerization when merely cooled to this temperature.

The stabilized solution was then shipped at low winter temperature for several days, and thereby solidified in slurry or pasty form. On reheating to 676 C. practically all of the product went back into the liquid condition exof formaldehyde was 44%. The solution was stored in an oven having aminimum temperature of '43 C. It I remained stable without formation of solid polymer,

- whereas in the absenceof thehydroxypropyl methyl cel- The pH of the solution may be varied, I 'but for best results should not be such as to cause precept for a very small proportion, which was removed. I

The product was then subjected to 17 similar cycles of solidification (at 21 C.) and liquefaction (at 66 C.);' substantially no further undissolved materialwas formed. In contrast, an otherwise identical formaldehyde solution without the hydroxypropyl methyl cellulose gave large amounts of insoluble material after one cycleof solidification and liquefaction and did not liquefy at all after two Example III ample I. 7 Example IV Example I was repeated twice, substituting 100 ppm.

Example V Example I was repeated except that the concentration lulose an oven temperature of 6065" 'C. was required to keep the. solution stable at this concentration. When cooled and heated as in Example II, the results were substantiallyrthe same as described inExample II.

Example VI I formulations were modified :by the use'of the,formalde hyde'solutions of this invention. I I

(a) 702.5 grams of the solution obtained in accordance with Example I (b) was mixed with 98.9 grams methanol, 5 cc. of a 50% aqueous solutioniof triethanolamine, 2 5v I Q cc. of 28% aqueous solution of ammonia, 330 grams of" ureaand 115.2 grams of flake 'paraformaldehyde and refluxed for 15 minutes at atmospheric pressure, then aci I dified with 2.5 cc. of 25% aqueous phosphoric acid I and 15.0 grams of phthalic-anhydride and further refluxed to give a water soluble urea formaldehyde resin of 10 0 cps. viscosity. A'sparklingclear and stable resin solution was produced.

the proportions used were:

and the resin was cooked to a viscosity of l 10 centipoises.

A sparklingly clear and stable resin solution wasp roduced.

(c) Example VI (a)"and (b) were repeated except that commercial 37 /z% methanol-inhibited formalin was employed in place of the methyl cellulose-containing formaldehyde solution; the amount of methanol separately added in the process was changed so that the total quantities ofmethanol present and the urea-formaldehydemethanol ratios, were the same asthose in Example VI (a) and (b), respectivelyyand slight changes were made in the proportions of the basic and acidic materials added,

Example VII 774 grams 'of the reheated solution. of Example lI (pH=4.3), 43.7 grams of water, 9 9 grams of methanol, and 5 cc; of a 50% aqueous solution oftriethanolarnine were agitated together; the mixture had a pH of 7.6; 25 cc. of 28% aqueous ammonia were then added so that the pH rose to 8.7. .Then'33O grams of urea were added, the mixture-Was heated to reflux at atmospheric pressure-and refluxed'at about 203 F. for 15 minutes;

the pH at thisstage was 7;8. 2.5 grams of. phthalic anhydride were added to reduce the pH to 4.5 and the'rnixture was refluxed at atmospheric pressure until a sample of the product startedxto turn cloudy when dropped in ice water (about 3 hours ofrefluxing). Then 15 'cc.-'of 50% aqueous triethanolaminewere added to bring the. pH to 7.1, obtained. V

7 Example VIII Example VH was repeated, using the s olution ofEx: ample V, with substantially the same results,

Example IX The colloid-containing solution of ExampleI washeat In this example conventional urea-formaldehyde resin (11') Example VI (a) was repeated, except that borax was used in place of 'the triethanolamine and ammonia,

A resin solution of unusuallyigood clarity was ed under a vacuum of 27-28 inches (corresponding to a pressure of about 75 mm. Hg absolute), while evaporating Water, and some formaldehyde, until the formaldehyde concentration of the residue reached 87%, at which time its temperature was 119 C. The hot clear liquid residue was a hard white solid on cooling. When the same distillation was carried out only until the formaldehyde concentration was 82% the hot clear liquid was a waxy soft solid on cooling.

Example X To freshly prepared aqueous solutions of formaldehyde of 46.89% concentration there were added 100 p.p.m. of one of the following colloids, respectively: Sure-Jell (a powdered pectin preparation manufactured by General Foods Corp., New York, N.Y., for making homemade jams and jellies, and containing fruit pectin together with dextrose and citric acid); water soluble Irish moss extractives (carrageenin, in mixed lambda and kappa forms, sold under the trademarke Sea-Kem of which various viscosity grades were tested including type 3 having a water viscosity of 90-125 MacMichael or about 400-570 centipoises', type 6 having a water viscosity 400-500 MacMichael or about 1800-2200 centipoises; type 8 having a water viscosity of 1020 MacMichael or about 45-90 centipoises; and type 14 having a water viscosity of 1040 MacMichael or about 45-180 centipoises); and calf gelatin (Knox gelatin). The resulting solutions were then maintained at 38 C. for 20 days; none of them showed observable polymerization during this period.

Example XI To a freshly prepared aqueous 42.5% solution of formaldehyde (produoed as in Example I) there were added the stabilizers described below in the amounts indicated below. The stability of each of the resulting solutions was tested by allowing it to stand at 73 F. At this temperature the same formaldehyde solution, to which no stabilizer was added, was unstable; i.e., it showed polymerization in less than one day:

(a) Hydroxypropyl methyl cellulose (cold water-soluble Methocel 65 HG of 4000 cps. viscosity when measured on a 2% solution in water at 20 C., and having a methoxyl content of 27-29% and a hydroxypropyl content of 4 to 7.5%) used in proportions of 10 p.p.m., 50 p.p.m., 100 p.p.m. and 1000 p.p.m., based on the weight of the formaldehyde solution. For the experiments using 10 p.p.m., 50 p.p.m. and 100 p.p.m. the stabilizer was added as a 1% solution thereof in water; the final stabilized formaldehyde solution was clear. For the experiment using 1000 p.p.m. the dry stabilizer was added directly to the formaldehyde solution; some of the added stabilizer remained undissolved at this concentration. The stability period in each case was over 30 days, after which the tests on the stable solutions were discontinued.

b) Methyl cellulose (cold water-soluble Methocel Technical having a methoxyl content of 26-33%). Grades of this material having viscosities of 1500, 4000, and 8000 cps. (when measured on 2% solution in Water at 20 C.) were used, each grade in proportions of 10 p.p.m., 50, p.p.m., 100 p.p.m. and 1000 p.p.m., based on the Weight of the formaldehyde solution. For the experiments using 10 p.p.m., 50 p.p.m. and 100 p.p.m. the stabilizer was added as a 1% solution thereof in water; the final stabilized formaldehyde solution was clear. For the experiment using 1000 p.p.m. the dry stabilizer was added directly to the formaldehyde solution; some of the added stabilizer remained undissolved at this concentration. The stability period in each case was over 30 days, after which the tests on the stable solutions were discontinued.

(c) Ethyl cellulose (Ethocel, standard, of ethoxy content 48-49.'5%, having a viscosity of about 200 cps., when measured on a solution in 80-20 tolueneethanol at 25 C.), used in proportions of p.p.m., 50

p.p.m., 100 p.p.m. and 1000 p.p.m., based on the weight of the formaldehyde solution. For the experiments using 10 p.p.m., p.p.m. and 100 p.p.m. the stabilizer was added as a 1% solution thereof in methanol; the final stabilized formaldehyde solution was clear. For the experiment using 1000 p.p.m. the dry stabilizer was added directly to the formaldehyde solution; some of the added stabilizer remained undissolved at this concentration. For the 10 p.p.m. proportion the stability period of the resulting formaldehyde solution was 4 days. For the other proportions the stability period in each case was over 30 days, after which the tests on the stable solutions were discontinued.

(d) Sorbitan monolaurate (Arlacel 20), used in proportions of 50 p.p.m. and 100 p.p.m. The stabilizer was incorporated by first dissolving it, in 5% concentration, in methanol, then adding water, and then adding the water-methanol solution to the aqueous formaldehyde solution in amount such that the final concentration of formaldehyde was 42%; the stabilized formaldehyde solution was clear. The stability periods were 3 days (for 50 p.p.m.) and 16 days (for 100 p.p.m.).

(e) Polyoxyethylene lauryl ether (Brij 30) used in proportions of 50 p.p.m., 100 p.p.m. and 1000 p.p.m. For the experiments at 50 p.p.m. and 100 p.p.m. the stabilizer was incoprorated by first dissolving it, in 5% concentration, in methanol, then adding water, and then adding the water-methanol solution to the aqueous formaldehyde solution in amount such that the final concentration of formaldehyde was 42%; the stabilized formaldehyde solution was clear. For the experiment at 1000 p.p.m. the Brij 30 was added directly to the aqueous formaldehyde and the resulting solution was hazy. The stability periods were 9 days (for 50 p.p.m.), 12 days (for 100 p.p.m.) and 13 days (for 1000 p.p.m.).

(f) Mixture of 5 p.p.m. Methocel HG (4000 cps.) and 5 p.p.m. Methocel, Tech. (8000 cps.). The stability period was over 18 days, after which the test on the stable stabilized solution was discontinued.

(g) Mixture of 5 p.p.m. Methocel 60 HG (4000 cps.) and 5 p.p.m. Brij 30. The stability period was over 18 days, after which the test on the stable stabilized solution was discontinued.

(h) Mixture of 10 p.p.m. Methocel 60 HG (4000 cps.) and 5 p.p.m. silicone antifoam emulsion (GE 60). The stability period was over 18 days, after which the test on the stable stabilized solution was discontinued.

(i) Mixture of 5 p.p.m. Methocel 60 HG (4000 cps.) and 5 p.p.m. Methocel 60 HG (50 cps.). The stability period was over 18 days, after which the test on the stable stabilized solution was discontinued.

(j) Mixture of 5 p.p.m. each of the viscosity grades 50 cps., 400 cps. and 4000 cps. of Methocel 60 HG. The stability period was over 18 days, after which the test on the stable stabilized solution was discontinued.

Example XII cc. of the unstabilized formaldehyde solution of Example XI was added to a solution of 0.1 gram of cellulose acetate stearate (soluble in acetone, p-dioxane, onitrotoluene and glacial acetic acid and not soluble, at concentrations above 1%, in methanol, butanol, benzene, 2,2,4-trimethylpentane or water) in 2 cc. of acetone. The resulting solution was allowed to stand at 73 F. After 12 days the cloudy solution was still stable and the test was discontinued.

Example XIII Example I (a) was repeated, with similar results, using aqueous formaldehyde obtained by oxidation of methanol in place of the aqueous formaldehyde obtained by oxidation of aliphatic hydrocarbon.

Example XIV Example XII was repeated, using as the stabilizer 100 p.p.m. of lipophilic glycerol sorbitan laurate (Atlas G- by Letters Patent is:

. V y 7 672, a light amber oily liquid whose HLP, Atlas, is 7.6). The stability period of the resulting formaldehyde solution was 7 days at 73 j Example X V 4 I 7 invention are;pres'ent there is lesstendency for deposits of solid polymer tolform onthe heated pipes or other 7 heated'containers used for transferring the "hot molten material;

This application is a continuation-in-part of. our copending application Serial 'No. 744,059, filed June 24,

1958, and now abandoned.

his to be understood that the foregoing detailed description isgiven merelyby way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure 1. A solution of 30 to 80% of formaldehyde inwater, said solution being stabilized by a dissolved organic colloid, said colloid being a high polymer and being present in a stabilizing amountup to about 1000 ppm.

'2; A solution of 30 to 80% of formaldehyde in water,

, said solution containing less than about 2% of methanol and being stabilizedv by a dissolved organic colloid, said colloid being a high polymer. and being present in a stabilizing amount up to about 1000 p.p.m.

3. A solution of 30 to 80% of formaldehyde in water, said solution being stabilized by a dissolved organic colloid, said colloid being a high polymer and being present in a stabilizing amount up'to .about 100 ppm.

' 4..A solution of 30m 80% of formaldehyde in water, said solution being stabilized by a dissolved organic colloid, said colloid beinga high polymer and being present in a stabilizing amount up to about 1000 p.p.m., said colloidbeing selected from the group consisting of methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, esters of cellulose with higher fatty acids, pectin, .carrageenin, polyoxyethylene ethers of higher fatty alcohols,

and gelatin,

2,153,526 Walker Apr.' 4, 1939* 2,237,240 Sponsel; Apr. l, 1941 2,245,491 Menger'etal. June 10'; 1941 2,267,290 .Somerville-etal. Dec. 23,1941 2,279,096 Sparre Apr. 7,1942

. 2,300,976 Scheuermann Nov. 3,-1942 2,486,399 Gararine Nov. 1, 1949 2,492,453 Yates V Dec. 27, 1949 2,538,051 Schick Ian. 16, 1951 2,586,098 Schibler Feb. 19,1952 2,632,740 Schibler Mar. 24,1953

' 2,834,676 Stanley et a1. a L.' 'May'13, 1958 FOREIGN PATENTS 7 420,993 Great Britain Dec. 12, 1934 5. A solution of 30 to of formaldehydein water,

said solution being stabilized by a dissolved water. soluble 9 2 'methyl cellulose, said methylcellulose being presentin a stabilizing amount up to about 1000 ppm.

6. A solution as set forthin claim 5,'wherein said water soluble methyl cellulose is hydroxypropyl methylfcellulose. Y Y

' I 7. A solution of 30 to 80% of formaldehyde in water, said solution containing. less than 2%. of methanol and a stabilizing amount up toabout p.p.m. of a dissolved water soluble methyl cellulose.

8. A solutionof 30to 80% of formaldehyde in water, 7

said solution-being stabilized bya stabilizing amount up to about l000,p.p.m. of ethyl cellulose.

9-. A solution" of 30 to 8 0% of formaldehyde in water, said solution being stabilized by a stabilizing amountlup 4 to about "1000 ppm, of carragee'nin.

10. A solution of 30to 80% of'formaldehyde inwater, said solution being stabilized by, astabilizing amount'up to about 1000 p.p.m. ofpectin.

11. A solution of 30 to 80% of formaldehyde 1; water, said' solution being stabilized by a stabilizing amount ,up

to about 1000 ppm. of a polyoxye'thylene-ether of a higher fatty acohol. 1

12. A solution of 30 to 80% of formaldehyde in water, said solution being stabilizedby a stabilizing amount up to about, 1000 ppm. of polyoxyethylene laurylether.

' References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES j Wilson The. Chemistry of Leather Manufacture, 2nd" Synonyms, 2nd ed. 1955), page 392T P9 H39. 1

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. $137,736 June 16 1964 Roy H Prinz et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patentshould read as corrected below Column 2 line 64 for "remains" read resins column 4, lines 37 and 38 for "wasp reduced" read was produced Signed and sealed this 10th day of November 1964c (SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Aitcsting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 131,736 June 16 1964 Roy Ho Prinz et a1,

7 It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patentshould read as corrected below.

Column 2, line 64L for "remains' read resins ,column 4 lines 37 and 38 for "wasp reduced" read was produced Signed and sealed this 10th day of November 1964,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A SOLUTION OF 30 TO 80% OF FORMALDEHYDE IN WATER, SAID SOLUTION BEING STABILIZED BY A DISSOLVED ORGANIC COLLOID, SAID COLLOID BEING A HIGH POLYMER AND BEING PRESENT IN A STABILIZING AMOUNT UP TO ABOUT 1000 P.P.M. 